The present invention relates to a valve actuator in an internal combustion engine, and, more particularly, to an appliance for valve actuation in an internal combustion engine, comprising a camshaft with at least one first cam and at least one second cam, an actuation lever driving a valve and driven by the first cam having a cam protrusion and a base circle, a coupling lever driven by the second cam having a cam protrusion and a base circle, the actuator lever and coupling lever being operatively supported on a lever pin so as to be pivotable relative to one another, a coupling appliance including a coupling element for coupling the actuator lever and the coupling lever, which coupling element is attached to one of the levers and is configured to act on the other lever with adjustment thereof via a force change, and, a device for preventing adjustment of the coupling element at one of a time and in a period predetermined by the position of the camshaft, including a change in force acting on the coupling element.
A valve actuator appliance is described in DE 34 45 951 C2 wherein an adjustment of the coupling element at an undesired time is prevented by an additional mechanical control lever which engages in the coupling element. This arrangement is expensive, subject to wear, heavy and requires additional installation space.
An object of the present invention is to provide a valve actuating appliance which prevents coupling of the actuation lever and the coupling lever at an undesired time or in an undesired period without involving substantial expenditure or additional weight and installation space.
This object has been achieved in a valve actuator appliance of the present invention by providing that the base circle of one of the two cams has a depression in the region in which the associated lever is in contact at the predetermined time or in the predetermined period.
In the device according to the invention, it is a particular advantage that neither additional weight nor additional installation space are introduced by the depression produced in a particular region of the base circle. Specifically, the depression in the base circle can have a circular configuration with a radius which is slightly smaller relative to the base circle. Low manufacturing costs result especially because the base circle depression does not have to have particularly accurate dimensions. The wear occurring during the slight additional motions is slight. Coupling between the two levers at an undesired time or in an undesired period is prevented in a simple manner in the present invention because, in contrast to the periods in which the two levers slide along on the base circle matched to one another, they are slightly pivoted relative to one another during the undesired periods and because, as a result, the coupling element attached to one lever cannot engage on the other lever. Undesired times and periods for the coupling of the two levers can occur because simultaneous coupling of a plurality of lever pairs has to be avoided or because a certain sequence has to be maintained in the coupling of the lever pairs or because it is necessary to prevent a small part only of the coupling procedure being carried out when the lever is loaded. As a result, wear and damage occur on the coupling appliance or, if the coupling is cancelled under load, on the lever and cam.
In one embodiment of the coupling element of the present invention, which can be actuated hydraulically or purely mechanically and which is easy to manufacture, the coupling is a preloaded pin guided on a lever and partially introducible into an opening in the other lever. The pin can be arranged in the actuation lever or in the coupling lever and the opening correspondingly in the other lever. It is also possible for the coupling procedure to be initiated by an increase or a reduction in the force acting on the pin.
The appliance according to the present invention, by the provision of a region of the base circle depression arranged immediately before the cam protrusion and extending to a crankshaft angle of about 90.degree., reliably prevents incomplete coupling of the actuation and coupling levers where this cannot be brought to a conclusion reliably because the cam protrusion subsequently becomes effective and force is transmitted between the two levers. A coupling introduced shortly before the region of the reduced base circle radius can be reliably concluded because the forces transmitted between the two levers in this region are, at most, slight.
According to another feature of the present invention, apparatus is provided for effecting the change in force within a second region of substantially less than 360.degree. of camshaft angle, which region remains constant with respect to position of the camshaft, a plurality of second cams is provided for actuating valves and have mutually offset cam protrusions, and the depression is arranged only in those of the second cams in which the second region overlaps with the time or period of undesired adjustment of the coupling element. The beginning of coupling is always located within a certain period so that, in the case of those cams for which the undesired time or period falls completely outside the first mentioned period, it is possible to economize by omitting the measure of reducing the base circle radius. Apparatus for fixing the time when coupling begins, which can be manufactured with little outlay and are easy to operate, include a switching valve inserted into a liquid conduit between a pressure source and the coupling element.
A favorable range for the depth of the base circle reduction is in the range of approximately 0.1 to 0.5 mm. On one hand, this depth reliably avoids coupling and, on the other, avoids an excessively strong deflection of the associated lever.
In an embodiment of the appliance in accordance with the present invention in which the base circle depression is arranged on the cam associated with the coupling lever, the reduction in the base circle radius has no influence whatsoever on the position of the associated valve or on the forces acting on the latter because, in the decoupled condition, there is no connection between the coupling lever and the valve and, in the coupled position, the position of the levers is determined by the cam with the unaltered base circle associated with the actuation lever. If a hydraulic valve clearance compensation element is associated, as usual, with the actuation lever, the arrangement avoids pumping up this element erroneously.